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wptrunner: A web-platform-tests harness

wptrunner is a harness for running the W3C web-platform-tests testsuite.


wptrunner is expected to be installed into a virtualenv using pip. For development, it can be installed using the -e option:

pip install -e ./

Running the Tests

After installation, the command wptrunner should be available to run the tests.

The wptrunner command takes multiple options, of which the following are most significant:

--product (defaults to firefox)
The product to test against: b2g, chrome, firefox, or servo.
--binary (required)
The path to a binary file for the product (browser) to test against.
--metadata (required)
The path to a directory containing test metadata. [1]
--tests (required)
The path to a directory containing a web-platform-tests checkout.
--prefs-root (required only when testing a Firefox binary)
The path to a directory containing Firefox test-harness preferences. [2]

The --metadata path is to a directory that contains:

  • a MANIFEST.json file (the web-platform-tests documentation has instructions on generating this file); and
  • (optionally) any expectation files (see below)
[2]Example --prefs-root value: ~/mozilla-central/testing/profiles.

There are also a variety of other options available; use --help to list them.

Example: How to start wptrunner

To test a Firefox Nightly build in an OS X environment, you might start wptrunner using something similar to the following example:

wptrunner --metadata=~/web-platform-tests/ --tests=~/web-platform-tests/ \
--binary=~/mozilla-central/obj-x86_64-apple-darwin14.0.0/dist/ \

And to test a Chromium build in an OS X environment, you might start wptrunner using something similar to the following example:

wptrunner --metadata=~/web-platform-tests/ --tests=~/web-platform-tests/ \
--binary=~/chromium/src/out/Release/ \

Example: How to run a subset of tests

To restrict a test run just to tests in a particular web-platform-tests subdirectory, use --include with the directory name; for example:

wptrunner --metadata=~/web-platform-tests/ --tests=~/web-platform-tests/ \
--binary=/path/to/firefox --prefs-root=/path/to/testing/profiles \


By default wptrunner just dumps its entire output as raw JSON messages to stdout. This is convenient for piping into other tools, but not ideal for humans reading the output.

As an alternative, you can use the --log-mach option, which provides output in a reasonable format for humans. The option requires a value: either the path for a file to write the mach-formatted output to, or "-" (a hyphen) to write the mach-formatted output to stdout.

When using --log-mach, output of the full raw JSON log is still available, from the --log-raw option. So to output the full raw JSON log to a file and a human-readable summary to stdout, you might start wptrunner using something similar to the following example:

wptrunner --metadata=~/web-platform-tests/ --tests=~/web-platform-tests/ \
--binary=/path/to/firefox --prefs-root=/path/to/testing/profiles
--log-raw=output.log --log-mach=-

Expectation Data

wptrunner is designed to be used in an environment where it is not just necessary to know which tests passed, but to compare the results between runs. For this reason it is possible to store the results of a previous run in a set of ini-like "expectation files". This format is documented below. To generate the expectation files use wptrunner with the --log-raw=/path/to/log/file option. This can then be used as input to the wptupdate tool.

Expectation File Format

Metadat about tests, notably including their expected results, is stored in a modified ini-like format that is designed to be human editable, but also to be machine updatable.

Each test file that requires metadata to be specified (because it has a non-default expectation or because it is disabled, for example) has a corresponding expectation file in the metadata directory. For example a test file html/test1.html containing a failing test would have an expectation file called html/test1.html.ini in the metadata directory.

An example of an expectation file is:

example_default_key: example_value

  type: testharness

    expected: FAIL

      if platform == 'win': TIMEOUT
      if platform == 'osx': ERROR

  type: testharness
  disabled: bug12345

The file consists of two elements, key-value pairs and sections.

Sections are delimited by headings enclosed in square brackets. Any closing square bracket in the heading itself my be escaped with a backslash. Each section may then contain any number of key-value pairs followed by any number of subsections. So that it is clear which data belongs to each section without the use of end-section markers, the data for each section (i.e. the key-value pairs and subsections) must be indented using spaces. Indentation need only be consistent, but using two spaces per level is recommended.

In a test expectation file, each resource provided by the file has a single section, with the section heading being the part after the last / in the test url. Tests that have subsections may have subsections for those subtests in which the heading is the name of the subtest.

Simple key-value pairs are of the form:

key: value

Note that unlike ini files, only : is a valid seperator; = will not work as expected. Key-value pairs may also have conditional values of the form:

  if condition1: value1
  if condition2: value2

In this case each conditional is evaluated in turn and the value is that on the right hand side of the first matching conditional. In the case that no condition matches, the unconditional default is used. If no condition matches and no default is provided it is equivalent to the key not being present. Conditionals use a simple python-like expression language e.g.:

if debug and (platform == "linux" or platform == "osx"): FAIL

For test expectations the avaliable variables are those in the run_info which for desktop are version, os, bits, processor, debug and product.

Key-value pairs specified at the top level of the file before any sections are special as they provide defaults for the rest of the file e.g.:

key1: value1

[section 1]
  key2: value2

[section 2]
  key1: value3

In this case, inside section 1, key1 would have the value value1 and key2 the value value2 whereas in section 2 key1 would have the value value3 and key2 would be undefined.

The web-platform-test harness knows about several keys:

Must evaluate to a possible test status indicating the expected result of the test. The implicit default is PASS or OK when the field isn't present.
Any value indicates that the test is disabled.
The test type e.g. testharness or reftest.
The type of comparison for reftests; either == or !=.
The reference url for reftests.